Determining the conversion efficiency of an exhaust gas catalytic converter

Abstract

In order to determine the conversion efficiency of at least one component of a catalytic converter box comprising at least one SCR catalytic converter and an oxides of nitrogen storage catalytic converter for the aftertreatment of the exhaust gases of an internal combustion engine, wherein the catalytic converter box is associated at the downstream end with a NO x sensor, at least for a limited period of time the internal combustion engine is operated such that a first of the two components does not affect the signal detected by means of the NO x sensor and the conversion efficiency of the second component is determined depending on the signal of the NO x sensor that is not affected by the first component.

1 . A method for determining conversion efficiency of at least one component of a catalytic converter box ( 6 ) comprising first and second components, wherein the first component is at least one SCR catalytic converter ( 7 ) and the second component is an oxides of nitrogen storage catalytic converter ( 8 ), for aftertreatment of exhaust gases of an internal combustion engine ( 1 ), wherein a NO x  sensor ( 9 ) is disposed downstream of the catalytic converter box ( 6 ), characterized in that at least for a limited period of time the internal combustion engine ( 1 ) is operated such that one of the first and second components does not affect a signal detected by means of the NO x  sensor ( 9 ) and the conversion efficiency of an other of the first and second components is determined depending on a signal of the NO x  sensor ( 9 ) that is unaffected by the one of the first and second components. 
     
     
         2 . The method according to  claim 1 , characterized in that for a limited period of time the internal combustion engine ( 1 ) is operated such that a reduction of the NH 3  stored in the SCR catalytic converter ( 7 ) occurs and if no or almost no more NH 3  is stored, the conversion efficiency of the oxides of nitrogen storage catalytic converter ( 8 ) is determined depending on the signal of the NO x  sensor. 
     
     
         3 . The method according to  claim 2 , characterized in that the internal combustion engine ( 1 ) is operated for the limited period of time such that the SCR catalytic converter ( 7 ) reaches a temperature at which the stored NH 3  is released. 
     
     
         4 . The method according to  claim 2 , characterized in that the internal combustion engine ( 1 ) is operated such that a feed of NH 3  to the SCR catalytic converter ( 7 ) is at least substantially prevented and a reduction of NO x  is carried out using the stored NH 3 . 
     
     
         5 . The method according to any  claim 1 , characterized in that the internal combustion engine ( 1 ) is operated at least for a limited period of time such that saturation of the oxides of nitrogen storage catalytic converter ( 8 ) with NO x  takes place, and if no or almost no more NO x  can be stored the conversion efficiency of the SCR catalytic converter ( 7 ) is determined depending on the signal of the NO x  sensor ( 9 ). 
     
     
         6 . The method according to  claim 1 , characterized in that the oxides of nitrogen storage catalytic converter ( 8 ) is loaded with NO x  at least until a NO x  slip is measured at the NO x  sensor, an operating mode is selected in which a fully operational or at least sufficiently operational SCR catalytic converter ( 7 ) would convert the entire NO x  concentration in the exhaust gas and the conversion efficiency of the SCR catalytic converter ( 7 ) is determined depending on the signal of the NO x  sensor ( 9 ). 
     
     
         7 . The method according to  claim 1 , characterized in that the NH 3  storage capacity of the SCR catalytic converter ( 7 ) is concluded depending on the signal of the NO x  sensor ( 9 ). 
     
     
         8 . The method according to  claim 7 , characterized in that NH 3  desorption owing to the NH 3  arising in the NO x  stored in the oxides of nitrogen storage catalytic converter ( 8 ) is taken into account when determining the NH 3  storage capacity of the SCR catalytic converter ( 7 ). 
     
     
         9 . The method according to  claim 7 , characterized in that NH 3  desorption owing to the NH 3  arising in the NO x  stored in the oxides of nitrogen storage catalytic converter ( 8 ) is suppressed by operating the internal combustion engine ( 1 ) before the detection of the signal of the NO x  sensor ( 9 ) such that the NO x  stored in the oxides of nitrogen storage catalytic converter ( 8 ) is released. 
     
     
         10 . The method according to  claim 7 , characterized in that the internal combustion engine ( 1 ) is operated with a rich fuel mixture, while the signal of the NO x  sensor ( 9 ) is analyzed for determining the NH 3  storage capacity of the SCR catalytic converter ( 7 ). 
     
     
         11 . The method according to  claim 7 , characterized in that the internal combustion engine ( 1 ) is operated with an only slightly rich fuel mixture, while the signal of the NO x  sensor ( 9 ) is analyzed for determining the NH 3  storage capacity of the SCR catalytic converter ( 7 ). 
     
     
         12 . The method according to  claim 7 , characterized in that the internal combustion engine ( 1 ) is operated with an only slightly rich fuel mixture, with a target lambda value greater than 0.97, while the signal of the NO x  sensor ( 9 ) is analyzed for determining the NH 3  storage capacity of the SCR catalytic converter ( 7 ). 
     
     
         13 . The method according to  claim 7 , wherein the oxides of nitrogen-storage catalytic converter ( 8 ) is disposed in the flow of exhaust gas upstream of the SCR catalytic converter ( 7 ), characterized in that the NH 3  store of the SCR catalytic converter ( 7 ) and the NO x  store of the oxides of nitrogen storage catalytic converter ( 8 ) are emptied and then by operating the internal combustion engine ( 1 ) with a rich fuel mixture, NH 3  is produced in the flow of exhaust gas and the signal of the NO x  sensor ( 9 ) is analyzed to determine the NH 3  storage capacity of the SCR catalytic converter ( 7 ). 
     
     
         14 . A non-transitory computer-readable medium storing a computer program ( 14 ) that when executed performs a set of functions for controlling an internal combustion engine ( 1 ), the set of functions comprising the steps of  claim 1 . 
     
     
         15 . A control unit ( 11 ) for controlling the operation of an internal combustion engine ( 1 ), the control unit ( 11 ) comprising:
 non-transitory computer-readable medium storing a computer program ( 14 ) that when executed in the control unit ( 11 ) controls an internal combustion engine ( 1 ) by performing the steps of  claim 1 .